The present invention relates to an ultrasonic flow meter for ultrasonically measuring a flow rate and/or a flow velocity of a gas or a fluid.
Conventionally, ultrasonic flow meters of this type are known in the art such as that disclosed in Japanese Laid-Open Publication No. 11-351926. As illustrated in FIG. 44, an ultrasonic flow meter includes measurement pipe 1 for allowing a fluid to flow from one end to the other end thereof, an upstream ultrasonic transducer 2a, and a downstream ultrasonic transducer 2b. The upstream ultrasonic transducer 2a and the downstream ultrasonic transducer 2b oppose each other via the measurement pipe 1 therebetween with a predetermined angle with respect to the center line of the measurement pipe 1. The upstream ultrasonic transducer 2a and the downstream ultrasonic transducer 2b are housed in depressions 3a and 3b, respectively, of the measurement pipe 1. A flow variation suppressing section 5 is further provided on an inlet side 4 of the measurement pipe 1. A fluid entering the measurement pipe 1 is regulated by the flow variation suppressing section 5 so as to reduce the inclination of the flow line in the measurement section and/or to suppress the generation of a vortex, thereby reducing the variation in the ultrasonic reception level due to the reflection and/or refraction of the ultrasonic wave at the interface of a flow disturbance, and thus preventing the measurement precision from deteriorating.
Other conventional examples are known in the art such as that disclosed in Japanese Laid-Open Publication No. 63-26537. As illustrated in FIG. 45, a pair of the ultrasonic transducers 2a and 2b are provided along the wall surface of the measurement pipe 1 respectively on the upstream side and the downstream side with respect to each other. The ultrasonic transducers 2a and 2b are housed in the depressions 3a and 3b, respectively, provided in the measurement pipe 1, with a bulk ultrasonically transmissive member 3c in the cavity space of each of the depressions 3a and 3b, so as to prevent a flow from entering the depressions 3a and 3b, thereby providing a high-precision flow rate measurement.
With the conventional structure as illustrated in FIG. 44, it is possible to reduce flow disturbances in the measurement section of the measurement pipe 1 and the depressions 3a and 3b by the flow variation suppressing section 5, thereby reducing the deterioration of the measurement precision. However, when the flow rate through the measurement pipe 1 increases, the fluid flows into the depressions 3a and 3b to cause a vortex, thereby increasing the flow disturbance between the ultrasonic transducers 2a and 2b. In such a case, the ultrasonic wave is reflected or refracted by the increased vortex, thereby lowering the ultrasonic reception level. Thus, it is difficult to reduce the driving input for the ultrasonic transducers 2a and 2b. 
With the conventional structure as illustrated in FIG. 45 in which the bulk ultrasonically transmissive member 3c is provided in each of the depressions 3a and 3b, a propagation loss may occur during the propagation of the ultrasonic wave through the bulk ultrasonically transmissive member 3a, thereby lowering the ultrasonic transmission output or the ultrasonic reception sensitivity. Moreover, because the ultrasonic wave is propagated through a solid as it passes through the bulk ultrasonically transmissive member 3a, the rectilinear property thereof is reduced so that it is difficult to radiate the ultrasonic wave toward the opposing ultrasonic transducer. Thus, it is difficult to reduce the power consumption of the flow meter so that it can be used as a device such as a gas meter for measuring the amount of a fuel gas for household use such as town gas or LPG which is used over an extended period of time, e.g., 10 years, with only a small electric cell capacity.
The present invention solves the above-described problems. An objective of the present invention is to reduce the generation of flow disturbances or vortices between ultrasonic transducers so as to enhance the ultrasonic reception level, thereby increasing the measurement precision and the upper limit value for the flow rate measurement, and reducing the power consumption by reducing the driving input for the ultrasonic transducers.
An ultrasonic flow meter of the present invention includes: a measurement flow path through which a fluid to be measured flows; ultrasonic transducers provided respectively on an upstream side and a downstream side with respect to each other along the measurement flow path; an upstream aperture hole and a downstream aperture hole, the aperture holes for exposing the ultrasonic transducers to the measurement flow path; a first influent suppressor provided in a vicinity of at least the downstream aperture hole for reducing inflow of the fluid to be measured into the aperture hole; a second influent suppressor provided on an upstream side of the measurement flow path with respect to the aperture holes for reducing the inflow of the fluid to be measured into the aperture holes; a measurement control section for measuring a propagation time of an ultrasonic wave between the ultrasonic transducers; and a calculation section for calculating a flow rate based on a signal from the measurement control section, wherein the first influent suppressor provided for the downstream aperture hole includes an aperture hole sealing section having at least one ultrasonically transmissive hole. Thus, it is possible to stabilize the flow between the ultrasonic transducers so as to enhance the ultrasonic reception level, thereby increasing the measurement precision and the upper limit value for the flow rate measurement, and to reduce the driving input for the ultrasonic transducers by the enhancement of the ultrasonic reception level and by improving the attenuation of the ultrasonic wave by providing the influent suppressor.
Another ultrasonic flow meter of the present invention includes: a measurement flow path through which a fluid to be measured flows; ultrasonic transducers provided respectively on an upstream side and a downstream side with respect to each other along the measurement flow path; an upstream aperture hole and a downstream aperture hole, the aperture holes for exposing the ultrasonic transducers to the measurement flow path; a first influent suppressor and a second influent suppressor for reducing inflow of the fluid to be measured into the aperture holes for both a forward flow and a reverse flow of the fluid to be measured; a measurement control section for measuring a propagation time of an ultrasonic wave between the ultrasonic transducers; and a calculation section for calculating a flow rate based on a signal from the measurement control section, wherein: the first influent suppressor provided for the aperture hole which is on the downstream side when the fluid flows in a forward direction is an aperture hole sealing section having at least one ultrasonically transmissive hole; and the second influent suppressor is provided on both an inlet side and an outlet side of the measurement flow path. Thus, even when the flow has a pulsation and causes a momentary reverse flow, it is possible to reduce, as in the case of a forward flow, the inflow of the fluid to be measured into the aperture hole, and to significantly reduce flow disturbances between the ultrasonic transducers, thereby increasing the measurement precision and the upper limit value for the flow rate measurement.
Another ultrasonic flow meter of the present invention includes: a measurement flow path through which a fluid to be measured flows; ultrasonic transducers provided respectively on an upstream side and a downstream side with respect to each other along the measurement flow path; aperture holes for exposing each ultrasonic transducer to the measurement flow path; a propagation path flow regulator provided along an ultrasonic wave propagation path between the upstream ultrasonic transducer and the downstream ultrasonic transducer and having a regulation section exposed to the flow; a measurement control section for measuring a propagation time of an ultrasonic wave between the ultrasonic transducers; and a calculation section for calculating a flow rate based on a signal from the measurement control section. Thus, the regulation section of the propagation path flow regulator arranged immediately upstream of the ultrasonic wave propagation path facilitates the disturbance of the flow across the entire zone from the upstream side to the downstream side of the ultrasonic wave propagation path. Therefore, in the ultrasonic wave propagation path, the flow condition is equally disturbed across the entire area of the ultrasonic wave propagation path along the width direction from an area near the upstream aperture hole to an area near the downstream aperture hole irrespective of the flow rate, whereby it is possible to reduce the changes in the correction coefficient across the entire flow rate measurement zone, thereby preventing increases in the error due to the correction coefficient and increasing the measurement precision. Thus, the measurement precision is maintained even when the Reynolds number changes due to the change in the kinematic viscosity of the fluid, whereby it is possible to realize a measurement device which is resistant against changes in the temperature of the fluid or changes in the composition of the fluid, thereby increasing the practicability of the device.
Another ultrasonic flow meter of the present invention includes: a measurement flow path through which a fluid to be measured flows; ultrasonic transducers provided respectively on an upstream side and a downstream side with respect to each other along the measurement flow path; aperture holes for exposing each ultrasonic transducer to the measurement flow path; a propagation path flow regulator provided along an ultrasonic wave propagation path between the upstream ultrasonic transducer and the downstream ultrasonic transducer and having a regulation section exposed to the flow; an influent suppressor for reducing inflow of the fluid to be measured into the aperture hole; a measurement control section for measuring a propagation time of an ultrasonic wave between the ultrasonic transducers; and a calculation section for calculating a flow rate based on a signal from the measurement control section. Thus, the regulation section of the propagation path flow regulator arranged immediately upstream of the ultrasonic wave propagation path facilitates the disturbance of the flow across the entire zone from the upstream side to the downstream side of the ultrasonic wave propagation path. Therefore, in the ultrasonic wave propagation path, the flow condition is equally disturbed across the entire area of the ultrasonic wave propagation path along the width direction from an area near the upstream aperture hole to an area near the downstream aperture hole irrespective of the flow rate, whereby it is possible to reduce the changes in the correction coefficient across the entire flow rate measurement zone, thereby preventing increases in the error due to the correction coefficient and increasing the measurement precision. Moreover, it is possible to arrange the influent suppressor for the aperture hole which opens into the measurement flow path so as to reduce the fluid flow into the aperture hole, thereby significantly reducing flow disturbances along the ultrasonic wave propagation path between the ultrasonic transducers and increasing the upper limit value for the flow rate measurement.
In one embodiment, the first influent suppressor provided for the upstream aperture hole is a flow deflector. Thus, it is possible to eliminate the propagation losses of the ultrasonic waves through the ultrasonically transmissive hole for the upstream aperture hole, thereby reducing the driving input for the ultrasonic transducers, and to reduce the flow of the fluid into the upstream aperture hole, thereby stabilizing flow disturbances along the ultrasonic wave propagation path and improving the measurement precision.
In one embodiment, the first influent suppressor provided for the upstream aperture hole is an aperture hole sealing section having at least one ultrasonically transmissive hole. Thus, it is possible to significantly reduce the inflow of the fluid into the upstream and downstream aperture holes, thereby increasing the upper limit value for the flow rate measurement and increasing the measurement precision even for a flow which is accompanied by a reverse flow. Moreover, it is possible to realize an ultrasonic transmission/reception with desirable S/N characteristics by the significant reduction in flow disturbances due to the aperture hole. Thus, it is possible to reduce the transmission output and the driving input, thereby reducing the power consumption.
In one embodiment, an aperture ratio of the aperture hole sealing section provided for the upstream aperture hole is greater than an aperture ratio of the aperture hole sealing section provided for the downstream aperture hole. Thus, propagation losses of the ultrasonic waves can be reduced, whereby it is possible to improve the upper limit value for the flow rate measurement and the measurement precision for a reverse flow, and to reduce the power consumption by reducing the driving input for the ultrasonic transducers.
In one embodiment, the propagation path flow regulator is arranged on the upstream side and the downstream side with respect to the ultrasonic wave propagation path. Thus, the ultrasonic wave propagation path is surrounded by the upstream and downstream propagation path flow regulators, whereby it is possible to equalize the disturbance condition from the upstream side and the downstream side of the ultrasonic wave propagation path, thereby further stabilizing the correction coefficient and further improving the measurement precision. Moreover, the influence of the flow condition on the downstream side along the measurement flow path is reduced by the downstream propagation path flow regulator. Thus, it is possible to realize a stable measurement irrespective of the piping condition on the downstream side of the measurement device, thereby improving the freedom in the installment of the measurement device. Moreover, the same effect is obtained both for a forward flow and a reverse flow along the measurement flow path, so that it is possible to stabilize the correction coefficient even for a pulsating flow, thereby increasing the measurement precision.
In one embodiment, the propagation path flow regulators arranged on the upstream side and the downstream side with respect to the ultrasonic wave propagation path are integrated together via a connector section. Thus, it is possible to prevent and stabilize a shift in the distance between the propagation path flow regulators or a positional shift between the upstream regulation section and the downstream regulation section, thereby realizing a measurement device with reduced variation. Moreover, the connecting section reinforces the propagation path flow regulators, whereby it is possible to reduce the size or the thickness of the regulation section. Therefore, it is possible to equalize the flow condition in the ultrasonic wave propagation path or to reduce the loss of pressure in the measurement flow path.
In one embodiment, the propagation path flow regulators arranged on the upstream side and the downstream side with respect to the ultrasonic wave propagation path and the influent suppressor are integrated together. Thus, it is possible to define the positional relationship, e.g., distance, between the upstream and downstream propagation path flow regulators and the influent suppressor, thereby stabilizing the flow condition. Therefore, it is possible to reduce the variations in the flow condition in the ultrasonic wave propagation path and to realize a stable measurement with little variation. It is possible by such integration to further increase the mechanical strength of the propagation path flow regulator, thereby preventing its deformation over a long term use and thus improving its durability and reliability.
In one embodiment, the influent suppressor is a first influent suppressor provided for the downstream aperture hole. Thus, the influent suppressor is arranged for the downstream aperture hole around which a strong vortex easily occurs because the downstream aperture hole extends in a direction at an acute angle with respect to the flow. Therefore, it is possible to reduce the fluid flow into the aperture hole so as to efficiently reduce flow disturbances between the ultrasonic transducers, thereby increasing the upper limit value for the flow rate measurement.
In one embodiment, the influent suppressor is a first influent suppressor provided for the upstream aperture hole and the downstream aperture hole. Thus, disturbances in the aperture hole, which account for a major part of the total flow disturbance in the ultrasonic wave propagation path, can be reduced efficiently, whereby it is possible to increase the measurement precision and the upper limit value for the flow rate measurement.
In one embodiment, the influent suppressor is a second influent suppressor which is obtained by providing the propagation path flow regulator arranged along the ultrasonic wave propagation path with an influent suppressing section. Thus, by the integration of the propagation path flow regulator with the influent suppressor, it is possible to reduce variations in the suppression of the fluid flow into the aperture hole, thereby increasing the reliability and allowing for provision of a compact ultrasonic wave propagation path. Therefore, it is possible to reduce the size of the measurement flow path.
In one embodiment, the influent suppressor includes a first influent suppressor provided for the aperture hole and a second influent suppressor obtained by providing the propagation path flow regulator with an influent suppressing section. Thus, the disturbance in the aperture hole is reduced by the multiplier effect of the first and second influent suppressors, and variations in the suppression of the fluid flow into the aperture hole are reduced by the integration of the propagation path flow regulator and the influent suppressor. Therefore, it is possible to increase the measurement precision and the reliability. Moreover, it is possible to provide a compact ultrasonic wave propagation path, thereby reducing the size of the measurement flow path.
In one embodiment, the first influent suppressor is an aperture hole sealing section having at least one ultrasonically transmissive hole. Thus, by covering the aperture hole with the aperture hole sealing section, it is possible to further increase the effect of suppressing the flow of the fluid to be measured into the aperture hole, thereby reducing and stabilizing the flow in the aperture hole.
In one embodiment, the first influent suppressor includes an aperture hole sealing section having at least one ultrasonically transmissive hole and a flow deflector provided in a vicinity of the aperture hole. Thus, it is possible to further increase the effect of suppressing the flow of the fluid to be measured into the aperture hole, thereby further improving the measurement precision. Moreover, it is possible by the provision of the flow deflector to reduce the attachment of foreign matter such as dust onto the aperture hole sealing section. Thus, the aperture hole sealing section can be selected primarily in view of the ultrasonic transmissivity without so much concern about the clogging of the aperture hole sealing section, thereby increasing the freedom of the selection. Moreover, it is possible to further increase the ultrasonic transmissivity so as to reduce the power consumption, or to further increase the sensitivity so as to realize a device with a desirable measurement precision.
In one embodiment, an aperture ratio of the aperture hole sealing section provided for the upstream aperture hole is greater than an aperture ratio of the aperture hole sealing section provided for the downstream aperture hole. Thus, propagation losses of the ultrasonic waves can be reduced, whereby it is possible to improve the upper limit value for the flow rate measurement and the measurement precision for a reverse flow, and to reduce the power consumption by reducing the driving input for the ultrasonic transducers.
In one embodiment, the aperture hole sealing section is a meshed member of an inclined mesh pattern having an inclination with respect to a horizontal direction. Thus, the pattern is inclined with respect to the horizontal direction, so that it is possible to facilitate settling of minute particles such as dust attached onto the inclined mesh portions, thereby reducing the amount of such minute particles deposited and thus preventing clogging of the meshed member. Therefore, it is possible to ensure propagation of the ultrasonic wave therethrough and to maintain a stable measurement precision over a long time, thereby improving the durability and reliability.
In one embodiment, the flow deflector is provided on the upstream side and the downstream side of the aperture hole. Thus, both for a forward flow and a reverse flow along the measurement flow path, it is possible to further improve the measurement precision, to suppress the flow into the aperture hole, and to prevent foreign matter from entering the aperture hole. Therefore, even for a pulsating flow which is accompanied by a reverse flow, it is possible to maintain a stable measurement precision over a long time, thereby improving the durability and reliability.
In one embodiment, a distance between the propagation path flow regulator and the ultrasonic propagation path is varied depending on a type of the fluid to be measured. Thus, it is possible to commonly use the measurement flow path irrespective of the type of the fluid to be measured by changing only the propagation path flow regulator, thereby improving the convenience, and to maintain a stable measurement precision irrespective of the fluid to be measured. Moreover, since the measurement flow path can be commonly used, it is possible to reduce the cost.
In one embodiment, the regulation section of the propagation path flow regulator is provided in the form of a meshed member. Thus, it is possible to reduce the installment space of the propagation path flow regulator with respect to the flow direction, thereby reducing the size of the measurement flow path.
In one embodiment, the regulation section of the propagation path flow regulator is provided in the form of a lattice member whose wall surfaces extend along the flow direction. Thus, it is possible to regulate the flow direction by the wall surfaces extending along the flow direction, thereby further equalizing the flow velocity distribution in the ultrasonic wave propagation path and thus improving the measurement precision.
In one embodiment, an interval between two adjacent regulation sections of the propagation path flow regulator is varied depending on a position along a transverse section of the measurement flow path. Thus, it is possible to optimize the size of each regulation section according to the position along the transverse section of the measurement flow path while maintaining a reduced length of the regulation section along the flow direction. Therefore, it is possible to further equalize the flow velocity distribution in the ultrasonic wave propagation path and reduce the length of the regulation section along the flow direction, thereby reducing pressure losses while improving the measurement precision due to the equalization of the flow velocity distribution.
In one embodiment, a cross section of the measurement flow path along a direction perpendicular to the flow therethrough has a rectangular shape. Thus, by employing the rectangular cross section, it is possible to increase the measurement area with respect to the total measurement cross-sectional area, thereby allowing for a flow measurement under the same condition from the upstream side to the downstream side of the ultrasonic wave propagation path. Moreover, it is possible to increase the two-dimensionality of the flow along the measurement flow path, thereby allowing for a high precision measurement of the average flow velocity of the fluid. Furthermore, it is possible to further increase the two-dimensionality of the flow by providing a second influent suppressor.
In one embodiment, a cross section of the measurement flow path along a direction perpendicular to the flow therethrough has a rectangular shape with an aspect ratio less than 2. Thus, it is not necessary to create a two-dimensional flow by increasing the aspect ratio, and it is possible to freely set the cross-sectional specification according to the height of the flow path such that interference by reflected waves is reduced, thereby allowing for ultrasonic transmission/reception with an increased sensitivity. Moreover, it is possible to reduce the loss of pressure in the measurement flow path by adjusting the measurement cross section such that the length along which the measurement cross section contacts the fluid is reduced without excessively flattening the measurement cross section.
In one embodiment, the aperture hole opens into the measurement flow path in a shape which has a side extending along a direction substantially perpendicular to the direction of the flow through the measurement flow path. Thus, it is possible to equally transmit/receive the ultrasonic wave with respect to the height direction of the measurement flow path, and to shorten the aperture length of the aperture hole in the measurement flow path along the flow direction. Therefore, it is possible to further reduce flow disturbances due to the aperture hole, thereby further improving the measurement precision.
In one embodiment, an introduction section arranged on the upstream side of the measurement flow path is provided with a non-uniform flow suppressor which has a passage opening with a minute aperture. Thus, it is possible to supply a stable flow into the measurement flow path irrespective of the shape of the flow path or the piping configuration upstream of the measurement flow path, thereby reducing flow disturbances between the ultrasonic transducers. Therefore, it is possible to further increase the upper limit value for the flow rate measurement and to further improve the measurement precision. Moreover, it is possible to realize a stable measurement irrespective of the shape of the flow path or the piping configuration upstream of the measurement flow path, thereby increasing the freedom in the installment of the measurement device.
In one embodiment, an introduction section arranged on the upstream side of the measurement flow path and an exit section arranged on the downstream side of the measurement flow path are each provided with a non-uniform flow suppressor which has a passage opening with a minute aperture. Thus, it is possible to supply a stable flow into the measurement flow path even when the fluid to be measured has a pulsating flow which is accompanied by a reverse flow or the fluid to be measured has a pulsation source on the downstream side. Therefore, it is possible to reduce flow disturbances between the ultrasonic transducers, to further improve the upper limit value for the flow rate measurement, and to further improve the measurement precision. Moreover, it is possible to realize a stable measurement irrespective of the shape of the flow path, the piping configuration, or the pulsation source, upstream or downstream of the measurement flow path, thereby further improving the freedom in the installment of the measurement device.
In one embodiment, a cross-sectional area of the introduction section or the exit section is greater than a cross-sectional area of the measurement flow path. Thus, it is possible to increase the installment cross-sectional area of the non-uniform flow suppressor so as to reduce pressure losses due to the non-uniform flow suppressor, thereby preventing increases in the pressure loss. Moreover, it is possible to increase the cross-sectional area of the introduction section or the exit section, thereby allowing for attachment of the measurement device without changing the shape of the introduction section or the exit section even when the shape of the flow path or the piping configuration on the upstream side or the downstream side is varied. Thus, it is possible to realize a measurement device with an increased freedom in the installment thereof.
In one embodiment, an aperture size of the passage opening of the non-uniform flow suppressor is less than an aperture size of a passage opening provided in the second influent suppressor. Thus, even when the upstream or downstream connection port is arranged with a positional shift, the fluid can equally flow within the measurement flow path, thereby allowing for a measurement with an increased measurement precision. Moreover, even when the fluid to be measured has a pulsation, it is possible to supply the fluid into the measurement flow path in a flow with a reduced pulsation due to the passage opening having a small aperture size, thereby improving the measurement precision even for a pulsating flow. Furthermore, due to the passage opening of the non-uniform flow suppressor having a small aperture size, it is possible to reduce the amount of dirt and/or dust entering the measurement section, thereby increasing the reliability of the measurement operation along the measurement flow path.
In one embodiment, another ultrasonic flow meter of the present invention includes: a measurement flow path through which a fluid to be measured flows; ultrasonic transducers provided respectively on an upstream side and a downstream side with respect to each other along the measurement flow path; and an upstream aperture hole and a downstream aperture hole, the aperture holes for exposing the ultrasonic transducers to the measurement flow path, wherein at least one of the aperture holes includes a plurality of partitioned paths extending along a propagation direction of the ultrasonic wave. Thus, since the ultrasonic wave propagates through the fluid within the partitioned paths, there is little decrease in the sensitivity. Moreover, due to the partitioning of the paths, it is possible to maintain the rectilinear property of the ultrasonic wave and to realize a desirable transmission/reception thereof. Furthermore, the aperture flow path within the aperture hole provided along the side surface of the flow path is divided into small parts, whereby a vortex is less likely to occur and it is possible to reduce the flow of the fluid into the aperture hole. Therefore, it is possible to properly measure the flow rate even when a pulsation occurs.
In one embodiment, at least one of the aperture holes includes a plurality of partitioned paths extending along a propagation direction of the ultrasonic wave. Thus, the fluid flow into the aperture hole can be reduced by the influent suppressor and the upper limit value for the measurement can be improved. Moreover, since the ultrasonic wave propagates through the fluid within the partitioned paths, there is little decrease in the sensitivity. Furthermore, due to the partitioning of the paths, it is possible to maintain the rectilinear property of the ultrasonic wave and to realize a desirable transmission/reception thereof. Moreover, the aperture flow path within the aperture hole provided along the side surface of the flow path is divided into small parts, whereby a vortex is less likely to occur and it is possible to further reduce the flow of the fluid into the aperture hole. Therefore, it is possible to properly measure the flow rate even when a pulsation occurs.
In one embodiment, each of the partitioned paths has an inlet surface extending along a vibration surface of the ultrasonic transducer and an outlet surface extending along a wall surface of the measurement flow path. Thus, since the ultrasonic waves can enter the partitioned paths at a right angle and thus travel therethrough in a straight path, an ultrasonic wave propagation path with no reflection and little attenuation is provided. Moreover, since the outlet is a flat surface with respect to the wall surface of the flow path, there is no disturbance in the flow in the periphery layer along the wall surface of the flow path. Furthermore, due to the alignment of the outlet surface as the radiation surface, it is possible to radiate the ultrasonic wave efficiently.
In one embodiment, each of the partitioned paths of one of the aperture holes extends colinearly with a corresponding one of the partitioned paths of the other aperture hole. Thus, the transmission surface and the reception surface are aligned with each other along the traveling direction of the ultrasonic wave, whereby it is possible to reduce the reflective attenuation thereof due to the partition plate in the partitioned paths of the opposing aperture hole.
In one embodiment, one side of a vertical section of each of the partitioned paths is longer than a half wavelength of an ultrasonic wave used for transmission/reception. Thus, the viscosity influence from the partition surface is reduced, whereby it is possible to provide partitioned paths with little attenuation.
In one embodiment, one side of a vertical section of each of the partitioned paths is not an integral multiple of a half wavelength of an ultrasonic wave used for transmission/reception. Thus, it is possible to suppress resonance in the lateral direction, thereby realizing an efficient propagation.
In one embodiment, a distance between the partitioned paths of the aperture hole and the vibration surface of a corresponding one of the ultrasonic transducers is an integral multiple of a half wavelength of the ultrasonic wave. Thus, resonance is provided at the half wavelength, whereby it is possible to provide an efficient radiation.
In one embodiment, a thickness of each partition of the partitioned paths is shorter than the wavelength of an ultrasonic wave used for transmission/reception. Thus, it is possible to prevent the reflection of the ultrasonic wave, thereby providing an efficient transmission/reception thereof.
In one embodiment, the partitioned paths are formed by fitting a honeycomb lattice into the aperture hole. Thus, by the employment of a lattice, it is possible to divide each aperture hole in the vertical and lateral directions.
In one embodiment, one of the partitioned paths has its opening at a center of the aperture hole. Thus, the aperture hole is aligned with the center of the ultrasonic transducer, thereby allowing for an efficient transmission/reception.
In one embodiment, a path length of each of the partitioned paths is shorter than the wavelength of an ultrasonic wave used for transmission/reception. Thus, it is possible to provide an ultrasonic wave propagation path with little attenuation.
In one embodiment, the partitioned paths are formed by arranging a net member in the aperture hole along a direction perpendicular to a propagation direction of the ultrasonic wave. Thus, by dividing the aperture hole with a net, it is possible to minimize the length of the path.
In one embodiment, each of the partitioned paths includes a communication section at a certain point along its length for communicating the partitioned path with an adjacent one of the partitioned paths. Thus, it is possible to minimize the attenuation due to the partition plates.